Yasworld

I am having this problem (i.e., Idling high and loud hissing noise when I'm not pressing the gas pedal). I just had the coolant pipe upgrade done on 2006 Porsche Cayenne Titanium.

What could be the problem? I will go back to the mechanic that did the upgrade, but I want to be sure what the problem is. This mechanic will most likely try to avoid taking responsibility for the issue.

I do have an extended warranty but it only covers the engine and major parts.

1. What do you think the problem could be?
2. Do you think it is an engine issue?

Any suggestions or direction will be helpful. Thanks!

JohnnyBahamas

If it runs without misfires, then it is almost certainly a vacuum issue. There is a soft hose at the back of the manifold and a hard plastic hose that runs down both fuel rails. Vacuum pressure sets the idle and the suction would explain the hissing.

But...

If it misfires on throttle application and/or is displaying a CHECK ENGINE light on the speedometer, then it could be a cut manifold gasket. The gasket is soft rubber and there is a sharp, metal, brass colored clip at the back of the driver's side cylinder bank that is used to hold the black vacuum hose in place. That clip can easily cut the manifold gasket when reinstalling the intake manifold. The hissing would then be that back cylinder (I don't remember the number) sucking air. But, if it is the gasket, the engine will run poorly, backfire explosively, and of course set off a CHECK ENGINE light.

Probably the vacuum hose at the back of the manifold came off or an piece of the vacuum hose system on top of the motor is cracked or cut.

Yasworld

Thank you soooo much. I will go back to the mechanic and let him know what's happening. I was hoping to sell this car soon and upgrading to the Panamera so this repair is really bad timing :-(. I will let you know the outcome. Again thanks for your quick reply.

bigbuzuki

Did you get an outcome?